Cleaning up GnuPG User ID validity in the test suite

[Daniel Kahn Gillmor]

In looking at the cryptographic features of the test suite, i noticed
that we're confusing user ID validity and key ownertrust (not an
uncommon confusion).  We're also not testing with a "normal" GnuPG
installation, which has the secret key we control typically set to
"ultimate" ownertrust.

This is a very nit-picky series without much of a functional
difference, but it makes the test suite more conceptually coherent
cryptographically, and should make future changes cleaner and more
sensible.

Signed-off-by: Daniel Kahn Gillmor <dkg at fifthhorseman.net>